Naturally occurring kaolin clays frequently include discoloring contaminants in the forms of iron-based ("ferruginous") and titanium-based ("titaniferous") impurities. The quantities of the titaniferous discolorants are particularly significant in the case of the sedimentary kaolins of Georgia, where such impurities are commonly present as iron-stained anatase and rutile. In the case of various crude kaolin clays, it is accordingly often desired and indeed, frequently imperative, to refine the natural product in order to bring the brightness characteristics thereof to a level acceptable for paper coating and other applications. Various techniques have been used in the past to effect the removal of the aforementioned discolorants. Thus, for example, hydrosulfites have been widely used for converting at least part of the ferruginous discolorants to soluble forms, which may then be removed from the clays.
Among the most effective methods for removing titaniferous impurities, including, e.g., iron-stained anatase, are the well-known froth flotation techniques. According to such methods, an aqueous suspension or slurry of the clay is formed, the pH of the slurry is raised to an alkaline value, for example by the addition of ammonium hydroxide, and a collecting agent is added, as for example, oleic acid. The slurry is then conditioned by agitating same for a relatively sustained period. A frothing agent, such as pine oil, is then added to the conditioned slurry, after which air is passed through the slurry in a froth flotation cell to effect separation of the impurities.
The aforementioned flotation technology, however, becomes of decreasing effectiveness as one attempts to utilize same to remove smaller and smaller discolorant particles. The difficulty in this regard is that the flotation forces are insufficient with respect to such small particles to overcome drag forces; and hence, the particles cannot adequately respond to the flotation treatment.
Within recent years it has further been demonstrated that high intensity magnetic separation techniques may be utilized for removing certain of the aforementioned impurities, including titaniferous impurities, and certain ferruginous matter. Anatase, for example, and certain other paramagnetic minerals, have been found to respond to high intensity magnetic fields. Thus, for example, U.S. Pat. No. 3,471,011 to Joseph Iannicelli et al., discloses that clay slurries may be beneficiated by retention for a period of from about 30 seconds to 8 minutes in a magnetic field of 8,500 gauss or higher. Reference may also be made to U.S. Pat. No. 3,676,337, to Henry H. Kolm, disclosing a process for treating mineral slurries by passing same through a steel wool matrix in the presence of a background field of at least 12,000 gauss. Various apparatus, such as that disclosed in Marston, U.S. Pat. No. 3,627,678, may be utilized in carrying out the Kolm processes. In this latter instance the slurry is thus passed through a canister, which contains a stainless steel or similar filamentary ferromagnetic matrix, while a high intensity magnetic field is impressed on the matrix by enveloping coils.
In certain further instances, as for example, in the teaching of U.S. Pat. No. 3,826,365, to V. Mercade, titaniferous impurities which are sought to be separated by a high-intensity magnetic field, are in advance of such separation, selectively flocculated. Somewhat similar phenomena are considered in Soviet Pat. No. 235,591 to Tikhanov, where several agents are used to selectively flocculate impurities in a slip of clay, which impurities are thereafter separated in a ferromagnetic filter including steel balls which have been previously rendered hydrophobic by treatment with a silicone compound.
All of the above magnetic separation methods, including those which employ differential flocculation, suffer from the limitation that particles with low magnetic susceptibility are not readily separated, despite the various technologies mentioned.
It may further be noted that in U.S. Pat. No. 3,974,067, to Alan J. Nott, which patent is assigned to the assignee of the present application, a method is disclosed for brightening a kaolin clay, wherein the clay as an aqueous dispersed slurry is subjected to a froth flotation treatment to remove titaniferous impurities, and the purified product from the froth flotation is thereupon subjected to magnetic separation by passing such product through a slurry-pervious ferromagnetic matrix postioned in a high intensity magnetic field. This method, while very effective compared to many prior art techniques, still retains certain of the limitations discussed in connection with flotation and conventional magnetic separation, i.e., small particle sized discolorants are floated only with difficulty, and particles of very low magnetic susceptibility cannot ultimately be removed by the magnetic separator stage of the process.
In a series of recent United States patents assigned to the assignee of the present application, a method has been disclosed for vastly increasing the effectiveness of magnetic separation methodology as same is applied to various minerals, including kaolin clays. In the techniques set forth in these patents, which include Nott et al U.S. Pat. Nos. 4,087,004, and 4,125,460, a dispersed aqueous slurry of the clay to be treated, is mixed with a finely divided magnetic particulate based upon magnetic ferrite particles. The slurry is thereupon passed through the aforementioned porous ferromagnetic matrix in the presence of an applied magnetic field, whereby contaminants seeded by the particulate are separated by the slurry. The said techniques are so effective that it is possible to obtain a high degree of brightening even with very low intensity applied fields. The U.S. Pat. No. 4,125,460 patent indeed discloses achieving of fully acceptable brightening at field intensities as low as 0.5 kilogauss.
Further pertinent art is disclosed in Shubert, U.S. Pat. No. 3,926,789, which teaches the selective separation of minerals by use of ferrofluids. In particular the ferrofluid is used to selectively wet a mineral component sought to be separated from a mineral mixture. In consequence the selected component is rendered of increased magnetic susceptibility, and is able to respond and be captured in the magnetic separator through which the mineral mixture is then passed.
Despite the fact that very minute discolorant particles can often not be recovered by the method, the aforementioned magnetic seeding methodology as disclosed in the Nott et al U.S. Pat. Nos. 4,087,004 and 4,125,460 patents above mentioned, has been among the most effective techniques thus far found to remove titaniferous and feruginous discolorants. Certain practical difficulties, however, are presented by commercial scale use of the said seeding technology. A principal one of these is that use of the magnetic seeding materials tends to produce relatively rapid fouling and blinding of the porous ferromagnetic matrix.
In particular, the magnetic separating apparatus which are most commonly utilized in the kaolin and other minerals processing industries, and which are generally of the type disclosed in the aforementioned U.S. Pat. No. 3,676,337, employ, as already mentioned, a matrix comprising fine steel wool. The magnetic ferrites (such as ferroso-ferric oxide) which are used as the magnetic seed, are of course, removed at the steel wool matrix during passage of the seeded slurry through the said matrix. In the usual procedures for utilizing these magnetic separators, the matrix is periodically flushed with the magnetic field extinguished, i.e., in order to remove and flush the discolorant materials and magnetic seed which have become accumulated in the matrix. In conventional magnetic separation technology, these flushing operations are highly effective, and the said apparatus can operate for months without any requirement for completely disassembling the apparatus for removal for thorough cleaning or replacement of the steel wool.
Magnetic ferrite particles, as for example the aforementioned ferroso-ferric oxide, have, however, a degree of residual magnetism. In consequence they are not easily flushed from the steel wool matrix, i.e., flushed during the normal flushing operations which occur in situ. In consequence, fouling and blinding of the steel wool matrices can occur with rapidity, necessitating relatively frequent disassembling of the separator apparatus and replacement or separate cleaning of the fouled matrix.
It may further be pointed out that certain of the magnetic seeding compositions include liquid organics. These materials can similarly accumulate in the matrix and cause contamination and fouling of same. In addition, certain of the organics, as for example, fatty acids which can be present with various ferrofluids, even if such compounds do not excessively foul the matrix, remain in the beneficiated output from the separator. Where such output is a coating clay, the said compounds can add highly undesirable properties. Oleic acid, for example, will introduce an undesirable frothiness into the coating clay, which will render same relatively unsuitable for most coating applications.
In accordance with the foregoing, it may be regarded as an object of the present invention, to provide a method for magnetically beneficiating clays by utilizing as one aspect thereof, magnetic seeding, which method removes discoloring titaniferous and ferruginous discolorants, to enable brightness improvements previously unattainable through prior art techniques based upon flotation, magnetic separation, or prior known combinations of same.
It is a further object of the present invention, to provide a method for magnetically beneficiating kaolin clays, which is so highly effective in removing titaniferous and iron-containing discolorants, as to enable production of coating quality clays from crudes previously deemed too contaminated for such ultimate use.
It is a still further object of the present invention, to provide a method as aforementioned, which is based upon use of magnetic seeding materials, and which method may be practiced utilizing conventional porous matrix magnetic separators, without rapidly fouling or blinding the said matrices.
It is a yet further object of the invention, to provide a method for magnetically beneficiating kaolin clays, which method employs magnetic seeding materials which are produceable at low cost, which are highly stable and storeable, and which therefore, are admirably suitable for commercial scale operations.
It is a still further object of the invention, to provide a method for magnetically beneficiating kaolin clays, which when utilized in conjunction with calcining, produces a product of yet exceptionally high brightness, without need for high calcining temperature as would tend to detrimentally increase abrasiveness of the clay pigment.